Why water fleas matter to farmers

Scrutiny of agricultural chemicals is nothing new. As far back as 1962, “we had pollution laws that focused mostly on sewage and nutrient problems,” said Richard Grippo, Arkansas State University professor of environmental biology.

1962 was also the year Silent Spring was published. “If you, as a farmer, want to get upset with any one person over the environmental movement, you probably should look at Rachel Carson,” said Grippo, who spoke at the Arkansas Soil and Water Education Conference in Jonesboro, Ark. “But, the truth is, she wasn't out to get farmers at all. She was just an astute person who wondered why there were sometimes flocks of dead birds lying by the road.”

Until that time, most people paid little or no attention to such things. “Carson recognized that whenever anyone sprayed for mosquitoes, dead birds would follow. She began looking into it, and what she found was that synthetic organic chemicals had caused much pollution. To make a long story short, environmental regulations were put in place on a whole host of things.”

Two points of focus

For water, though, the focus was on two things: point source pollution (from a specific source, like a pipe) and non-point source pollution (from run-off, for example).

“One of the ways to evaluate pollution sources is by detecting what biological effects the chemicals are causing. There are several ways to test toxicity. First is the acute test that is done in short order — usually four days. It's essentially a kill 'em and count 'em kind of testing.”

Researchers expose an organism to certain waters to see if it lives or dies. This is a “nice, quick way” to screen many chemicals.

The second approach is to study the long-term effects — anywhere from a week to three years — of chemicals in the environment. Often that includes measuring reproduction.

“After all, if a species can't reproduce it's in serious trouble.”

Why a flea?

For the long-term water tests, the obvious test subject most people think of is fish. The problem with fish, though, is that even the fastest-growing species take three to six months to go through a life cycle.

“To do things a bit faster, we study small invertebrates,” said Grippo. “We key in on the water flea because it goes through a complete life cycle in only three days.”

The water flea has forelimbs that sweep particles of food into its mouth. The food often will carry pollution if any is present. The water flea carries a brood sack, holding babies.

“We can measure how healthy an environment is by measuring how many babies a water flea has over a week's time… The water flea can act as a surrogate for all the organisms in this environment. The fleas are absolutely reliant on clean water — if there's a problem, they're going to let us know about it. They might not die, but they'll begin to have fewer babies very quickly.”

Having a look

In the past, lots of problems have been associated with irrigation. One that got the interest of the federal government involved a refuge in California where fish and aquatic birds began experiencing birth defects and generally decreased reproduction.

“They traced the problem back to agricultural runoff that was high in selenium. Do we have such a problem in Arkansas irrigation water? A few years ago, we wanted to have a look.

“Van McNeeley is a former graduate student of mine. Before that, though, he was an Extension agent in Poinsett County, Ark. In that position, he was interested in studying the environmental effects of rice farming. I suggested checking the re-lift water for irrigation: does doing so cause a toxicity problem? After all, the more you use water, the more concentrated chemicals and nutrients should become in it.”

The study, begun in 1997, was on three rice farms. The hard part was finding three producers willing to cooperate, said Grippo.

“I tip my hat to those farmers. They took a risk. If we'd found a problem, people would be pointing a finger at them, saying, ‘Hey, you're the one who got us in trouble!’”

The setup

“Typically farmers who use re-lift water pump water out of the ground, run it across the field, pick it up in a ditch and then pump it out to irrigate the crop again.”

Grippo and McNeeley wanted to know if the practice is healthy, harmful or benign to the environment. To that end, they gathered samples at three times during the season: at first flood, just after the last nitrogen application at midseason and then just prior to draining for harvest. They sampled at inlet and outlet points.

For a control, “we looked at water fleas grown in water developed and carefully controlled in the lab to provide the best conditions for the fleas.”

The mean results for 10 water fleas studied at each location and time show that their populations, after one week, “ranged from a high of 250 to lows of around 75 or 80.”

“In looking at our data, my mind was blown. The optimal control results, when compared to those from the re-lift outlet water were stunning: the fleas' reproduction in the re-lift outlet water went up by nearly 300 percent.

“The re-lift water isn't making the water fleas unsafe or unable to reproduce. They love it!”

That trend continued with the re-lift inlet samples as well. “The fleas didn't care for it quite as much as the outlet, but they still loved it. That's amazing and was seen across all three farms.”

The study was repeated several years after the initial data collection. Results were very similar.

Conclusions

The study is significant, insists Grippo.

“It shows the rice water is good for the water flea. Increased reproduction occurs throughout the growing season and, at least, over several years. The main point is that rice re-lift irrigation water doesn't pose an environmental risk. If EPA comes knocking and asks, ‘Have you looked at this water? Is there a problem with it?’ We can say, ‘Yes, we looked at it, and no there is no problem.’ Now, those cooperating farmers look like heroes.”

Of course around every silver lining, there's a cloud.

“The cloud here is not (understanding) why reproduction increased. At this point, we haven't nailed down the reason. It's probably some micronutrient that rice fields hold that the fleas are utilizing.”